This invention relates generally to a fuel vapor separator and more particularly to a fuel vapor separator for a high pressure fuel pump assembly of a combustion engine.
Combustion engines utilizing fuel injection systems for delivering fuel to the combustion chambers typically include a fuel pump assembly having a high pressure fuel pump and a vapor separator which acts as a fuel reservoir for supplying fuel directly to the high pressure fuel pump. The fuel pump delivers the fuel to a closed loop or recirculating fuel rail from which the fuel injectors draw fuel. A fuel pressure regulator controls the fuel pressure within the rail and is commonly mounted on the return or downstream end just prior to the fuel being returned into the vapor separator which is held at a substantially lower pressure.
For two-cycle engine applications, the fuel pump assembly commonly has a remote low pressure diaphragm fuel pump which is actuated by pressure pulses received from the crankcase of a running engine. The low pressure fuel pump delivers fuel from a remote fuel tank to the vapor separator, and often through a fuel filter mounted just upstream of the vapor separator. Again for two-cycle engine applications, the fuel pump assembly may include an oil injection pump or device which emits measured amounts of oil directly into the crankcase for lubrication and on occasion into the fuel reservoir of the vapor separator to achieve cleansing and lubrication of the fuel injectors. An oil gallery may also be mounted to the fuel pump assembly which routes oil from the oil pump to bearings contained within the crankcase chamber.
Unfortunately, the fuel entering the fuel chamber of the vapor separator from the fuel rail is often heated to excessive temperatures which if not addressed would substantially reduce the pumping efficiency of the high pressure fuel pump and create excessive fuel vapors which can lead to vapor lock within the rail, or injectors, causing the engine to run rough or stall altogether. The fuel is heated by exposure of the fuel rail to the heat being dissipated from the nearby engine block of a running two or four cycle engine, by the heat generated from any electrical solenoids of the running injectors, and from the energy produced by the electrical high pressure fuel pump, especially when the pump is rated at 24 or 48 volts. The generation of fuel vapor becomes pronounced when the pressurized hot fuel flows past the pressure regulator and dumps into the vapor separator at a much lower pressure, near atmosphere. The vapor is released through a vapor outlet passage carried by the vapor separator, and the liquid fuel within the vapor separator is cooled by a liquid coolant. The vapor outlet passage is open and closed by a float device which actuates upon low and high fuel levels within the fuel chamber of the vapor separator. The low pressure diaphragm fuel pump provides make-up fuel to the fuel chamber to stabilize fuel levels as the high pressure fuel delivers fuel from the vapor separator.
The coolant flows through a jacket or annular coolant chamber which surrounds the fuel chamber and is defined radially between a sleeve and an exterior housing. The sleeve is made of a heat conductive metal and performs as a structural barrier to keep the fuel and water separated and to promote the conduction of heat from the hot fuel to the colder coolant. For marine engine applications, such as personal or pleasure watercraft and outboard engine applications, the coolant is typically water. When the water flows directly from the body of water that the watercraft floats in, the coolant chamber of the vapor separator is exposed directly to either fresh (non-salt) or salt water. Either form, and especially salt water is corrosive to a variety of metals, therefore, to promote heat transfer yet reduce corrosion, the sleeve is made of expensive stainless steel, or aluminum having a corrosion resistant coating.
Because the water or coolant chamber is annular in shape, areas of stagnate water are present within the chamber which creates hot spots and degrades heat transfer from the fuel chamber to the coolant chamber.
A fuel pump assembly for use with a fuel injected combustion engine has a liquid cooled vapor separator from which conditioned fuel is drawn by a high pressure fuel pump. The vapor separator has an internal heat conductive sleeve which defines a fuel chamber or reservoir. A coolant chamber surrounds the heat conducting sleeve and is disposed between an exterior housing of the fuel pump assembly and the internal sleeve. A baffle, preferably coiled, is disposed within the coolant chamber and forms a coolant channel which spirals about the exterior of the sleeve. The channel has a first end which communicates with a coolant passage inlet and an opposing second end which communicates with a coolant passage outlet carried by the housing. The introduction of the baffle channels coolant flow through the preferably spiraling channel which improves the fuel cooling efficiency of the vapor separator. The baffle eliminates hot spots created by stagnate or non-flowing coolant areas within the coolant chamber.
Preferably, the housing is an integral part of the fuel pump assembly and supports the high pressure fuel pump along with numerous other components such as a fuel filter and a low pressure diaphragm fuel pump. The sleeve extends axially between an upper cap and opposite lower cap of the vapor separator. The upper cap carries a vapor outlet passage which opens on reservoir low fuel level and closes on reservoir high fuel level via a float device contained within the fuel chamber. The lower cap is preferably a unitary part of the housing.
Because the coolant may be salt water, which is particularly corrosive when heated, the sleeve must not only transfer heat from the fuel chamber to the coolant chamber, but it must be resistant to corrosion. Therefore, the sleeve is preferably made of metal such as stainless steel or aluminum having a corrosion resistant coating. Should the baffle be formed unitary to the sleeve, the sleeve is preferably made of a heat conductive injection molded plastic.
Objects, features and advantages of this invention include a vapor separator having a significantly improved cooling efficiency via introduction of a baffle. The invention may be readily incorporated into existing fuel pump assembly designs, improves high pressure fuel pump efficiency, reduces the potential for vapor lock within the fuel system, is of relatively simple design and economical manufacture and assembly and in service has a significantly increased useful life.